Intermittent Fasting: TRF, ADF, & WDF

You’ve no doubt recently been hearing the buzz about intermittent fasting, so what’s the deal?

Caloric restriction methods have become popular to support weight management, health, and even athletic performance. One of the most popular methods to accomplish caloric restrictions is Intermittent Fasting (IF). IF uses regular, short-term fasts with the goal of improving body composition and overall health. IF is a broad term used to encompass a number of specific programs, but most forms of it can be divided into the following categories:

Time-restricted feeding (TRF)

Alternate-day fasting (ADF)

Whole-day fasting (WDF)

Most IF programs use modified fasting rather than true fasting. True fasting requires abstinence from all caloric intake, but modified fasting allows small amounts of caloric intake. Occasionally, IF programs target specific macronutrient restriction or intake. Even during modified fasting, the total energy consumed is drastically lower than weight maintenance energy needs. In a nutshell, modified fasting can be viewed as following a very low–calorie diet but only on certain days or parts of days.

While most studies on IF have been done only on animals, mostly mice, it should be noted that recent studies provide substantial data showing IF promotes the increase and maintenance of fat free mass (FM), the decrease in fat mass (FM), and improved sensitivity and increased levels of hormones. That’s why we find it so darn intriguing!

Types of IF Explored

If we’re going to break this down, we first need to understand everything we’re talking about. Here’s an overview of different IF methods/types:

TRF: Time-Restricted Feeding – This is also called the Warrior Diet or Leangains method. It typically consists of following the same eating pattern each day, with certain hours comprising the fasting period (12–20 hours) and the remaining hours comprising the feeding window.

ADF: Alternate-Day Fasting – This method alternates between unrestricted eating days and pseudo-fasting days that allow one meal containing approximately 25% of daily calorie needs.

WDF: Whole-Day Fasting – Also called Eat Stop Eat, this method consists of one to two days of fasting per week and unrestricted eating on the other days.

Each of the above provides a unique approach to fasting that can be modified based on the specific needs of the faster. For example, when utilizing the TRF method, one might simply choose to cut off feeding after dinner, say around 6 p.m., and not feed again until the next morning at 6 a.m. Maybe you’re already following this method and didn’t even know it!

When it comes to the ADF method, you might choose to restrict your evening or morning caloric intake on fasting days. It’s worth noting that many who practice this fasting method report they focus on particular macronutrient profiles during these periods such as food or food combinations predominantly providing only protein and carbohydrate, only protein and fat, or only carbohydrate and fat. So if you find yourself interested in trying it, make a mental note.

WDF might be considered a little less structured as the unrestricted portion of the plan sets no parameters around macronutrient or caloric intake. With that in mind, this method does give you room to experiment within WDF, utilizing TRF and ADF methods on designated WDF fasting days.

How and Why IF Can Be Beneficial

Let’s get down to the nitty-gritty of IF. During short-term fasting, a transition in substrate utilization occurs. Reliance on carbohydrates decreased while there is an increase reliance on fatty acids. Whole body lipolysis and fat oxidation increases throughout the first 24 hours of food deprivation as blood glucose levels decline. Between 18 and 24 hours of fasting, it has been shown to yield a 50 percent decrease in glucose oxidation and a 50 percent increase in fat oxidation. Possible contributors to this shift in substrate utilization is theorized to be due to an increase in sympathetic nervous system activity, increase in growth hormone concentrations, and decrease in insulin concentrations -- In other words, it changes your body – for the better!

Will You Lose Muscle When Fasting?

We get it, you work hard for your muscles and you don’t want to sacrifice them to fasting – it’s a major concern for a lot of people. After all, we know that in starving people, muscle is broken down to provide a substrate for gluconeogenesis. While it is true that humans adapt to prolonged starvation by conserving body protein, it is also true that increased proteolysis (aka, breakdown of proteins into smaller amino acids and polypeptides) has been seen during short-term fasting studies; however, the majority of these studies compared measurements taken after an overnight fast versus those taken 60+ hours later. Because the duration of fasts during popular IF protocols is considerably shorter than 60 hours (i.e., up to 24 hours), it is possible that muscle mass loss does not occur to the same extent during shorter fasts. So don’t freak out – you’re not going to lose muscle mass as long as you do IF the right way!

It should also be noted that early literature examining complete fasting reported that catabolization of protein did not begin to increase until the third day of fasting. Some researchers have found that two weeks of ADF (alternating between 20-hour fasting and 28-hour feeding) did not alter whole-body protein metabolism in lean healthy men. These metabolic changes are interesting and it should be noted that the effects of habitual short-term fasts may be different than brief periods of short-term fasting in individuals who typically follow a normal eating pattern. Remember, sources count -- studies specifically examining IF protocols which also includes tracking body composition changes are going to be the best evidence regarding the effectiveness of these programs.

Which Method Yields the Best Results?

We wish we could make this easy for you, but the truth of the matter is that there is no “one size fits all” when it comes to this stuff. That, compounded with the lack of research specifically examining the effects of implementing IF programs in humans, makes it difficult to provide concrete recommendations on what approach works most effectively.

Nutrition and fitness programming needs to be tailored to the individual and should be designed based on goals and needs. However, several points are worth considering in the grand scheme of things. Intermittent fasting can be an effective means of reducing calorie intake, body weight, and body fat. For recreational exercisers, IF programs can be designed to allow adequate nutrient consumption before and after physical activity, just remember that exercise does not have to be performed in a fasted state when an IF program is implemented.

As for athletes, IF forms can be modified to fit an athlete’s training schedule. For example, ADF and WDF (i.e. the modified fasting days consisting of very low-energy intake) can be used less frequently or placed on rest days or days with lighter training activities. A TRF schedule can be developed allowing the athlete to eat at the most critical times, such as before and after training sessions and competition. Even incorporating a one day each week of modified fasting could help an athlete achieve a negative energy balance for the week while not disturbing the usual pattern of food intake on heavier training and/or competition days.

A Few More Things to Consider

You must remember that your intake of protein and the monitoring of body composition are important when utilizing IF methods.

When it comes to protein, it’s become clear that the amount of protein you eat per day is important, but what might be more important is how much you eat per meal and how you distribute those meals. Intermittent fasters have to take into account that when it comes to optimizing muscle mass, over-consuming protein once a day can’t make up for low-protein the rest of the time. In other words, eating small amounts of protein over the course of a day and then one whopping meal full of protein won’t balance out. If you’re looking to build muscle, then you need to make sure you’re consuming protein appropriately.

As far as body composition is concerned, you’d be crazy not to want to find ways to measure your IF success and meet your body composition goals. So, what’s the best way to do that? First and foremost, the scale isn’t going to be the right measure, especially if you’re building muscle. Remember, muscle weighs more than fat, so building muscle can make the numbers on the scale actually increase. Body measurements are a useful tool to help track your progress, such as measuring your body composition to calculate the percentage of your weight that is lean muscle mass and fat mass. Utilizing methods that can help you differentiate lean mass versus fat mass will help you determine if what you’re doing is actually working.

IF can be a useful tool if you know how to use it right! Remember to find sources you can trust to help lead your charge into the world of intermittent fasting. No bro-science!